A geofilter is a special overlay for Snaps that are only available in specific geographic locations which users can access and use in these select locations.
The interesting aspect of the geofilter is that they can be generated by Snapchat, by users or by brands (although the overlays must be approved by Snapchat before being made available). Geofilters can be created and paid for with specific time periods and geographic locations. For example, if you were hosting an event in your library a customised geofilter could be created for use by your attendees.
Geofilters are now available in the US, the UK and Canada.
[Update: this infographic shows the latest user numbers for Snapchat and explains the business benefits of a Snapchat presence.]
Source: Social Media Today.